(a) Field of the Invention
This disclosure relates to an apparatus and a method for plasma ion implantation of a solid element. More particularly, this disclosure relates to an apparatus and a method for plasma ion implantation of solid elements, which may implant ions of non-gaseous elements at room temperature into the surface of a sample.
(b) Description of the Related Art
In general, to improve durability of metal material or parts, coating of a high strength thin film such as titanium nitride on the surface of metal material, ion nitriding or ion carburizing, etc. are performed. However, in the case of the thin film coating, the coating layer may be separated due to weak adhesion to base material, and in the case of the ion nitriding or ion carburizing, parts may be easily heat-distorted due to high process temperature.
And, ion implantation which accelerates ions with high energy and injects them on the surface of material is performed. The ion implantation is a technology for accelerating ions to several tens to hundreds of keV so as to be entered on the surface of material, and it may form a modified layer to several thousands of Å below the surface of material, and form a gradual composition change layer, and thus, coating layer separation due to difference in material is not basically generated. Other advantages of the ion implantation are that it is not thermodynamically limited because it is a high energy process, there is no size change of a sample due to temperature increase or deterioration by heat because it is a room temperature process, and surface roughness is not largely influenced. Furthermore, the kind, thickness, and modification degree of a modified layer may be easily controlled by controlling the kind, energy, and amount of implanted ions.
However, despite many advantages of the ion implantation technology, the use of the ion implantation is very limited in the fields of materials except semiconductor. The reason therefore is as follows: The existing ion implantation apparatus has been developed for the purpose of impurity doping on a planar semiconductor wafer sample, and it extracts ions from ion source and accelerates them so as to be entered in the sample in the form of ion beams, and ion beams should be rastered for uniform ion implantation. A method of implanting ions in the form of ion beams has technological disadvantage including a necessity of masking to prevent sputtering by inclinedly entering ions and three-directional rotation of a sample for ion implantation to a three-dimensional object such as a mold, a tool, a machine element part, etc. because of fundamental limitation of Line-of-sight implantation. The above disadvantages, together with very expensive equipment cost compared to the other surface modification equipments, make practical application of the ion implantation technique difficult.
To overcome the disadvantages of the ion implantation technology in the form of ion beam, plasma ion implantation technology using plasma and high voltage pulse has been suggested (U.S. Pat. No. 4,764,394, Korean Patent No. 137704, European Patent No. 480688, Canada Patent No. 2052080, U.S. Pat. No. 5,126,163), which is a technology capable of uniformly implanting ions on the surface of a three-dimensional sample with large area to achieve surface modification. Specifically, since it uses plasma and high voltage pulse, it is not limited by ‘Child-Langmuir current limit’ and thus speed of uniform ion implantation to a sample with large area is very rapid, and ion beam rastering equipment is not required. And, since it uses plasma, charging on the surface of a sample does not substantially exist, and since the equipment is simple, clustering with other thin film process equipment is excellent and the equipment cost may be lowered.
However, most plasma ion implantation technologies so far suggested and used are capable of ion implantation of only a gas state such as nitrogen, oxygen, argon, methane, etc., and it cannot implant plasma ions of an element existing in a solid state. Although some prior art U.S. Pat. No. 5,777,438, U.S. Pat. No. 5,126,163) discloses plasma ion implantation of a solid element using pulsed cathodic vacuum arc, in case pulsed cathodic arc plasma is used, macroparticles of large size (droplet) are generated due to the arc and deposited on the surface of an ion implantation sample, and to prevent this, a filter using a magnetic field should be used.